I am new to IFS, so this may not be the best answer. 

It may sound archaic, but depending on the frequency, you could simply record the hours/costs in another program (Excel, etc..) and then use a ‘dummy’ item set with cost and price of $1, which can be easily calculated to total cost through quantity in the CO.

You may try a non-inventory sales part (with or without cost) and code the posting control to COGS account.

I propose you use a sales charge with cost only (sales price 0), the sales charge type cost can via M69 M70 be posted towards suitable accounts and counter accounts. The charge may be connected to a specific order line or just be a generic order based charge.

We use sales charge a lot, the good thing about those is that you can affect sales prices on order line level both positive and negative as well as cost (both positive and negative), fixed amount or percentage also possible. 

Please be aware of this

• you cannot put a sales charge in an agreement or price list, however you can set it per default to a part and/or customer 
• you cannot adjust the charge description in standard
• when printing, even though the sales charge is not set to printable, a summary will appear on the invoice and order confirmation unless you modify the reports and/or the application messages.